It has been known for a long time to set the thickness of the printing blankets for offset printing by means of grinding processes. The elastomeric flexographic printing forms are also ground on cylinder grinding machines for this purpose; here, the abrasion of the elastomeric material takes place, for example, via a grinding stone. In machines of this type, a grinding stone or grinding disc is used. By way of this, punctiform abrasion of the material by way of grinding takes place, in relation to the width of the grinding stone or the grinding disc. Here, the grinding is always performed after the vulcanization of the mixture of the elastomeric material; in this way, the mixture is fully cured and can be machined with the removal of material. The grinding can be carried out in one or more working processes.
It is disadvantageous here that vibrations occur repeatedly in the grinding machine as a result of the very highly crosslinked mixture in the case of hard, carbon black-filled elastomeric rubber mixtures (black mixtures), for example made from EPDM (ethylene propylene diene monomer or else ethylene propylene diene rubber) with a Shore A hardness of over approximately 45 ShA. The vibrations can build up and reinforce one another and are then evident as chatter marks or else vibration marks in the surface finish, that is, on the surface of the printing form. The inhomogeneous surface finish is visible in the varnish and in the ink transfer and therefore represents a quality defect.
In the case of very soft mixtures, for example made from SBR (styrene butadiene rubber) with a Shore A hardness of below approximately 45 ShA, the dimensional accuracy during grinding is continually a problem because of the extremely soft mixture.